In current large scale integrated circuits, there is a constant effort toward improving operating conditions or parameters, but a number of these improvements tend to conflict with each other. Linewidths and element sizes have constantly been reduced, in order to increase the density so as to make possible new integrated systems of greater versatility, capacity and capability. Such increases in resolution and in the number of circuit elements have, however, concomitantly increased the amount of heat generated internally, which directly impacts upon electron mobility and signal propagation times in the circuit. This not only decreases the data rate capability of the system but tends to introduce timing and other instabilities, which are unacceptable in these systems.
The dense integrated circuits are mounted on circuit boards via which external circuit couplings are made, and the geometry of the circuit packaging must permit access for purposes of servicing, inspection and repair. In order to do this, the circuit boards are often disposed in parallel adjacent planes with small spacings between them. They must also ba plugged in and detached repeatedly, and any associated system must fit within the allotted spaces and also engage in and detach from the active components or subsystems.
To achieve desired performance characteristics, the active elements in dense integrated circuit units are preferably maintained under subcooled conditions, as in the range of -50.degree. C. While this can be done by environmental cooling, that is, reducing the surrounding temperature to a desired level, such level would have to be substantially below -50.degree. C. in order to prevent localized heat buildup at the integrated circuits to a component temperature that is above -50.degree. C. Thus, the technique of cooling a large volume so as to drop the ambient temperature is both too expensive and cumbersome for most applications.
It has been proposed to reduce the cooling load that an ambient system would require by generating a subcooled fluid at a region spaced apart from the circuit units, as by use of a two-stage refrigeration system, and then piping this subcooled fluid to heat sinks in thermal contact with the active circuits. Heat losses can be substantial with this approach and it is necessary to minimize such losses by using state of the art decouplers in the fluid connections. These decouplers require special insulation designs and can only be disconnected and reconnected with care and effort. Furthermore, to reach the needed refrigeration levels such a system requires the use of two different refrigerants and special heat transfer circuits. Because a single refrigeration system may have to cool a number of integrated circuit units, such an arrangement is both costly to build and operate and also of low efficiency.
There is another requirement that complicates the refrigeration problem for integrated circuits. In the event of power or other failure, a backup system should come into operation to allow steady state operation of the integrated circuits at rates slower than the optimum but still acceptable at a temperature level which minimizes thermal buildup above the ambient. Such a support or backup system must itself be automatic and function without independent power for adequately fail-safe operation. The backup system also must fit within the geometry of the circuit boards and not interfere with engagement and disengagement of the boards.
Consequently it is evident that an improved refrigeration system for large scale integrated circuits is needed that is compact, thermally efficient, capable of easy disassembly, and provides an-automatic backup or support capability.
A related but distinct problem is posed by high performance personal computers, which are increasingly of smaller size but higher performance and which have only a convective cooling capability if that. To dissipate increasingly higher wattage heat loads in such systems, there is a need for a smaller high efficiency heat exchange system that can be adjusted to different size and geometry constraints.